Short wave receiver arrangement



May 7, 1935; H, M. 1. w|s

v SHORT WAVEYRECEIVER ARRANGEMENT Filed Sept. 25-, 1931 w M w R mu n MIM m 0 m n IM A D L mm AM w 52 mm 5320mm Sw x m 0 Q \QN Patented May .7,1935 UNITED STATES 2,000,084 snon'r wave RECEIVEB'ARRANGEMENT HaroldMiller Lewis, Douglaston, N, Y., assignor to Hazeltine CorporationApplication September 25. 1931, Serial No. 565,025

' 2 Claims. (01. 250-20) The present invention relates to ashort wavetuning system known as a short wave converter, for use in conjunctionwith a radio broadcast receiver. Such a converter operates to receiveshort wave signals and convert them, on the superheterodyne principle,into currents of a frequency within the frequency range of the broadcastreceiver. Thisfrequency will be referred to hereinafter as theintermediate frequency. The broadcast receiver serves as an intermediatefrequency amplifier and audio signal output.

In operation, the broadcast receiver is tuned to some frequency withinthe broadcast band, and it may be that the frequency selected is thesame as that being used by some transmitting station within the range ofthe receiver. However it is to be understood that it is not desired toreceive such a signal at that time, but to receive some short wavesignal, using, however, the frequency of the undesired signal as theintermediate fre- In operation, the usual converter receives andamplifies signals of the frequency to which the broadcast receiver isset to'respond and it also permits the reception of undesired signalswhich beat with the intermediate frequency produced by the converter andcause unpleasant interference. 1 Y

The broadcast receiving apparatus is itself usually shielded and wouldnot receive the signal directly, but, however, the undesired signal, ifit were of considerable strength, might be picked up on the lead orconnection between the converter and the broadcast receiver, or might,in 35 fact, be picked up by the antenna and be amplifled by themodulator of the converter and passed through the connection to thebroadcast receiver. It is the object of the present invention toovercome the above noted difliculty in connection 40 with the use of theconverter method of short wave reception, and to provide means forpreventing the receptionof signals of the intermediate frequency towhich the broadcast receiver is tuned, whether such signals are directlypicked 5 up or come through the converter itself. This and furtherobjects of this invention will become apparent from the followingspecification taken in connection with the appended claims and theaccompanying drawing.

50 In accomplishing the object of the present invention the leadsbetween the converter and the broadcast receiver, as well as the wiringand circuit elements of the converter itself, are completely shielded.In addition, the antenna input 65 circuit of the converter is providedwith a trap which would act as an amplifier thereof. 5

The plate supply of the modulator tube contains a tuned radio frequencychoke which is tuned roughly to the intermediate frequency and therebytends to by-pass currents of frequencies differing greatly from theintermediate frequency,

and which have been received by the converter. Having thus -brieflydescribed the elements comprising the present invention, attention isinvited to the accompanying drawing in which the single figurerepresents a circuit diagram of a converter embodying the presentinvention.

Referring now more particularly to the drawing, the antenna circuitincludes the antenna ill, the ground I I, the trap circuit i2,comprising the inductance l3 and condenser M, the primary winding l5,and a portion of the secondary windingit. The inductance i3 and thecondenser H of the trap circuit i2 are so proportioned that said circuitis resonant to the intermediate frequency produced by the short waveconverter. The input circuit of the converter is connected to the gridof modulator device H, which may be any thermionic tube, though thatshown is of the screen'grid type. The input circuit is tuned by means ofthe condenser 2|, which may be .a double condenser employing, as shown,a single rotor and two stators so arranged that the capacity obtainedbetween the rotor and one stator is'maximum, when the capacity betweenthe rotor and the other stator is minimum. The con- 36 nections to thestators are controlled by means of the switch 23. The actual condenserincludes two stators and two rotors, so arranged that when onerotor isentirely within its stator, the other rotor is entirely out of itsstator. This is 40 fully described in the application of William A.MacDonald, for Condensersfl Serial No. 564,997, filed concurrentlyherewith. Ihe function of the condenser and switch arrangement will beexplained later.

The tapped secondary I6 is connected by means of switch 24, so that anyof the tapped portions of the secondary may be included in theinputcircuit. The switch is so connected that the unused portions of thewinding are short-circuited.

.For producing the heterodyne frequency for combining with the incomingsignal and thus producing the intermediate frequency, there is providedthe oscillator 25. This oscillatortube is of the single grid type and.includes in its grid 3 circuit the secondary of the oscillationtransformer, the primary 42 of which is connected in the plate circuitwhich includes stopping condenser 43. The secondary 40 is a tappedwinding similar to IE of the antenna transformer, and the connections tosaid secondary are controlled by means of switch 34. The grid return ofthe oscillation circuit is completed through the biasing resistor 21,which is connected to the cathode of the tube 25. The frequency of theoscillation circuitis determined by means of condenser 3|, which issimilar to condenser 2|, and is connected to be operated therewith in auni-control manner by means of the control knob 22 associated with theindicator dial 26.

The connections to the'two portions of the condenser 3| are controlledby means of switch 33.

Padding condensers 4| M and S are provided across the two portions ofcondenser, as shown, for the purpose of aligning the oscillation circuitwith the input of modulator I1 in the middle wave range and short waverange, respectively. Padding condenser 4IL is connected across the longwave portion of the inductance winding 40, so that when the switch 34 ison contact L this condenser is practically in shunt with the condensers3| and US for adjusting the alignment in the long wave range. When theswitch 34 is on contact M, the condenser 4IL is in shunt with condensers31 and 31', and the total series capacity is at that time the sum ofthese three condensers.

In series with condenser 3| are provided series condensers 36, 31 and38, the connections to which are controlled by means of the switch 35.Each of these condensers is provided with the padding condenser 36',31', or 38, respectively, for the purpose of correcting the alignment ofoscillator circuit with the modulator input in the various frequencybands. In the middle frequency band, as has just been stated, thecondenser 4 IL is in shunt with 31 and 31. Coupling coils 44 and 45coupled to the middle and long Wave portions of the secondary 40,respectively, are included in the cathode circuit of the modu lator I 1.This circuit also includes the biasing resistor 46 shunted by by-passcondenser 41 for the purpose of causing tube H to act as a modulator.

The plate and screen grid potential are provided by means of the powersupply source 20 which, as shown, is of the ordinary double waverectifier and filter type. This power supply also provides heatercurrent for heating the cathodes of tubes l1 and 25. A resistor 29 isincluded in the plate lead of the modulator 25 for the purpose ofreducing the plate potential thereof.

The circuit elements of the converter are shielded as indicated by thedot-dash line which encloses them in the drawing. Any appropriateshielding means may be used. For instance, the usual metal chassis,which is constructed to enclose and shield the various elements attachedto it, may be used.

As shown, the dial 26 includes three scales, 26a, 26b, and 26-c, thesescales covering the short wave band, middle wave band, and long waveband, respectively.

It is to be noted that in order to get better spacing of the frequencyindicator, the short wave scale is placed in the outer position on thedial 26, as the condenser motion to get the frequency separationrequired to separate the various stations is less in the short wave handthan it is in the long wave band.

For the purpose of indicating in which of the' frequency ranges theconverter is operating, each of the scales is provided with one of theilluminating lights 1la, 11-12, or 1lc, controlled by means of switch 39to light them when tuning through the short wave band, middle wave band.

and long wave band, respectively.

Switches 23, 24, 33, 34, 35 and 39 are so arranged as to besimultaneously operated and also to be actuated by the control knob 22as the condensers are tuned through the limiting capacities for one ofthe frequency bands. Thus, the rotation of the control knob22 results inthe actuation of the switches 23 and 33, resulting in switching of theconnections to condensers 2| and 3|, respectively, to give the oppositecapacity extreme for the modulator and oscillator circuits. Switch' 39is simultaneously operated changing the lighting of the indicatinglights and thus indicating the change in the frequency band by changingthe indication from one to another of the scales. The specific means foractuating the switches constitute no part of the present invention, butare described fully in application of Harold Miller Lewis for Switchingarrangement, Serial No. 565,026, filed concurrently herewith.

Included in the plate supply to the modulator I1 is the inductance 50.This inductance may have a high inherent capacity as indicated bycapacity 5 I, or an actual condenser may be placed in shunt therewith.The inductance and capacity, however, are so proportioned thatfrequencies differing greatly from the desired, intermediate frequencywill be by-passed.

A connection from the output of modulator I1 is made through condenser52 and lead 53 to the antenna binding post of the receiver 51. Thisconnection is made through a shielded cable 54, which may, for example,be a BX cable, from the walls of which the lead 53 is spaced by means ofbakelite spacers 56. This spacing is necessary to prevent loss of signalenergy, and to prevent too high a capacity in the connection between theconverter and the receiver 51.

Also connected through the cable 54 is the ground connection 55, whichis connected to the ground binding post of receiver 51. The capacity 52and the inherent capacity between the leads 53 and 55 are soproportioned that they constitute a dummy antenna to properly load themodulator I1, and to prevent misalignment of the input of receiver 51.tween the antenna l0 and the lead 53 by means of which the antenna maybe directly connected to the input of the receiver 51 when it is desiredto receive signals in the broadcast band directly on receiver 51.

The receiver 51 may be of any well known type, and is provided with theusual sound reproducing device 58. The specific details of neither 51nor 58 constitute any part of the present invention.

The receiver is tuned to the intermediate frequency which it is desiredto utilize, preferably 1,000 kc. The direct reception of signals of1,000 kc., when the set is being operated to receive short wave signalsby means of the converter, is

prevented by means of the shielded cable 54. The

modulator is prevented from acting as an amplifier of signals of 1,000kc. frequency by means of trap circuit l2. Any signals of a frequencyother than 1,000 kc. in the output of modulator 11 would be by-passedthrough the inductance 50. It is thus seen'that a number of provisionshave been made to prevent the interference of broad- Switch 59 isprovided be-- cast signalswith the short wave signals'being received bymeans of the converter.

In the event that the converter constructed in accordance with thepresent invention is made to cooperate with any specific broadcastreceiver,

.the inductance l3 and condenser ll of the wave trap I! may be matchedto the tuning inductances and condensers, respectively, of the receiverso that the wave trap may be tuned by a similarsetting of its controlelement to any wave length to which the receiver is adjusted.

If it is desired, the converter and broadcast receiver may be combinedin a single unit, and in this case the condenser M may be connected tobe operated simultaneously with the tuning condensers of the broadcastreceiver II, as indicated by the dotted line connecting it and thebroadcast receiving condenser generally indicated at C. with thisarrangement, therefore, signals of the wave length which the broadcastreceiver is at any instant set to receive are, by the simultaneoustuning of the trap circuit, automatically prevented from reaching themodulator of the converter to beamplified thereby.

To recapitulate, the circuit It acts to prevent currents of theintermediate frequency being received over the antenna II and amplifiedby the modulator II, the shielding of the lead It prevents a directpick-up between the output of the device I! and the input of the radiobroadcast receiver, and the shielding of the converter prevents thepick-up within the converter itself.

It is obvious that a band-pass fiiter might be used in place of thesimple wave trap shown. In

this case the complete broadcast band wculd be excluded from theconverter so that the intermediate frequency could be changed as desiredto prevent interference with a particularly strong broadcast signal. 1

Full details of the above described circuits, including thecharacteristics thereof, are given in the copending application ofHarold Miller Lewis for Short wave converter, Serial No. 565,024, illedconcurrently herewith.

Full details of the mechanical arrangements for actuating the variousswitch mechanisms are given in the application of Harold Miller liewisfor Switching arrangement", referred to above.

I claim:

1. Short wave receiving apparatus which comprises a converter, forconverting short wave signals into long wave signals, said converterincluding a trap circuit comprising a fixed inductance and a variablecondenser in its input circuit for preventing impressing signals of along wave length directly upon the input of said converter, a radiobroadcast receiver connected to .said converter, and means connectingthe tuning elementof said wave trap with the tuning element of saidbroadcast receiver, whereby saiclv trap circuit will be simultaneouslytuned to the wave length to which said broadcast receiver is tuned toprevent impressing-signals of the long wave length by said converterupon said broadcast receiver.

2. In a radio receiver including a first portion adjustably resonant tosignal frequency voltages, a second portion variably resonant tovoltages substantially different in frequency from those of said firstportion, selective impedance means connected in said first portion andtuned to the frequency of said second portion to reject from saidreceiver signal voltage of the frequency of the signal voltageof saidsecond portion, and uni-control means for simultaneously tuning saidsecond portion and said selective impedance means of said first portion.

' HAROLD MILLER LEWIS.

